azygos vein vs vena

azygos vein and vena both are nouns.

Word	Noun	Adjective	Verb	Adverb
azygos vein	Yes	No	No	No
vena	Yes	No	No	No

As nouns, vena is a hypernym of azygos vein; that is, vena is a word with a broader meaning than azygos vein:

azygos vein: one of a system of veins that drain the thoracic and abdominal walls; arises as a continuation of the right ascending lumbar vein and terminates in the superior vena cava
vena: a blood vessel that carries blood from the capillaries toward the heart

Other hypernyms of azygos vein include vein, venous blood vessel.

azygos vein (noun)	vena (noun)
one of a system of veins that drain the thoracic and abdominal walls; arises as a continuation of the right ascending lumbar vein and terminates in the superior vena cava	a blood vessel that carries blood from the capillaries toward the heart